1. Field
Embodiments relate to an image forming apparatus including a transfer roller to charge paper such that a developing agent is adsorbed to the paper and a method of controlling the same.
2. Description of the Related Art
An electrophotographic type image forming apparatus uses a transfer member to feed a toner image generated by a developing member to recording media, i.e. paper. A corona mode and a transfer roller mode are known as transfer modes. The transfer roller mode is mainly used in consideration of miniaturization of image forming apparatuses and ozone generation in the corona mode.
In the transfer roller mode, transfer bias is applied to the transfer member, i.e. the transfer roller, to generate a transfer field and transfer is electrostatically performed according to the transfer field. In the transfer roller mode, however, paper may be contaminated by the transfer roller if the transfer roller contains contaminants before the paper contacts the transfer roller. For this reason, the transfer roller may be cleaned.
A first method of cleaning the transfer roller is to provide a cleaning member to clean the transfer roller. Specifically, a cleaning blade or a cleaning roller is disposed at the rear of the transfer roller to clean the transfer roller. However, this method needs additional devices and is thus not suitable for miniaturization and reduction of cost. Furthermore, the cleaning member may increase torque of the transfer roller and thus negatively affect jitter.
A second method of cleaning the transfer roller is an electrostatic cleaning method of applying transfer bias to the transfer roller to clean the transfer roller. After or before transfer of a toner image, cleaning bias is applied to the transfer roller to remove toner from the transfer roller. Specifically, cleaning bias having the same polarity as toner and cleaning bias having a polarity opposite to that of the toner are alternately applied to the transfer roller. As a result, toner charged with positive (+) and negative (−) polarities may be removed from the transfer roller.
When the transfer roller is cleaned in the transfer bias mode, uncharged paper powder or non-polar toner with an external additive removed therefrom is not removed. Furthermore, if the transfer roller is partially contaminated, the transfer roller is not uniformly charged with the result that image quality may be deteriorated and cleaning may not be completely achieved.